Automated data storage libraries are known for providing cost effective storage and retrieval of large quantities of data. The data in automated data storage libraries is stored on data storage media that are, in turn, stored on storage cells, shelves or the like inside the library in a fashion that renders the media, and its resident data, accessible for physical retrieval. Such media is commonly termed “removable media”. Data storage media may comprise any type of media on which data may be stored and which may serve as removable media, including but not limited to magnetic media (such as magnetic tape or disks), optical media (such as optical tape or disks), electronic media (such as PROM, EEPROM, flash PROM, Compactflash™, Smartmedia™, Memory Stick™, etc.), or other suitable media. Typically, the data stored in automated data storage libraries is resident on data storage media that is contained within a data storage cartridge, also referred to herein as a cartridge. An example of a data storage cartridge that is widely employed in automated data storage libraries for mass data storage is a magnetic tape cartridge.
In addition to data storage media, automated data storage libraries typically contain one or more data storage drives that store (write) data to and/or retrieve (read) data from the data storage media. Transport of cartridges between storage cells and storage drives is typically accomplished by one or more robot accessors. Such accessors have grippers for physically retrieving a selected cartridge from a storage cell within the automated data storage library and transporting the cartridge to a storage drive by moving in the X and/or Y directions.
While there are numerous ways in which different mechanical components in a library may fail, an important and potentially damaging incident occurs when a data cartridge is on the floor of the library, such as by being dropped the accessor/gripper. If the cartridge remains on the floor, it may interfere with movement of the accessor and possibly even cause the accessor to become jammed or derailed, resulting in a major library failure. Even if the accessor does not become jammed or derailed, if the library is not “aware” that the cartridge has dropped, the data contained on the cartridge is unavailable and essentially lost, at least temporarily.
If the accessor is transporting a cartridge to a storage drive to be read from or written to and the drive does not indicate that it has received the cartridge, the library controller can execute a “lost cartridge state” error recovery procedure (ERP) in which the source and/or destination locations may be checked for the cartridge by the accessor. If the checked locations are empty, the cartridge is assumed to be either in the gripper or on the floor. To determine which, the library controller may initiate a “put” operation in which the gripper attempts to put a cartridge into a drive or storage cell. However, trying to manipulate a potentially defective or damaged gripper or accessor is certainly not desirable and may cause further damage.
Consequently, a need remains for a safe and efficient method and system to detect cartridges on the floor of the library.